Digital Theses Archive


Tesi etd-04242017-151547

Type of thesis
Stiffness tuning in Soft Robotics.
Scientific disciplinary sector
INGEGNERIA - Biorobotics
relatore Prof. LASCHI, CECILIA
  • Nessuna parola chiave trovata
Exam session start date
The need for building a new generation of robots using soft materials comes out from considerations regarding the main limitations of traditional robots in negotiating natural environments with respect to the compliance and adaptability demonstrated by animals. Nature teaches that inherent softness enables dexterity and safe cooperation, but stiffness is required for effective exchange of forces during interactions with the environment. <br>Taking inspiration from biological systems, the focus of soft robotics research has been entirely devoted to the design and development of innovative actuation strategies for an on-demand control of such deformability and compliance. <br>In literature, two different approaches for achieving this goal emerge: the first one, typically experienced when working with soft materials-based actuators, exploits the stiffening implied in the material deformation when actuation happens, while the second one refers to the capability of inducing a change in the elastic modulus, without motions.<br>In the framework of this Ph.D. thesis, the second approach has been investigated. In particular, passive, active and semi-active stiffness tunings have been studied in two robotic applications. The first strategy plays with intrinsic mechanical properties of the soft material in order to get a specific stiffness value; the second one takes advantage of an antagonistic arrangement of the actuators in the soft system for determining stiffness modulation; the third one uses semi-active technologies to dramatically change the intrinsic passive mechanical properties of the material itself.<br>The most suitable soft actuation technologies have been identified and their working principles have been tested with respect to technical requirements, in order to define advantages and limitations. Once the range of the suitable soft technologies has been mastered, new design concepts have been proposed as solutions for stiffness tuning in the framework of the following applications:<br>(i) The development of a vocal fold prototype as the first, fundamental, step for a human larynx simulator, based on the specifications given by the research group in otorhinolaryngology of the Pisa University hospital led by Prof. Ursino. The passive response of the multi-layered structure has been investigated by capitalizing on the intrinsic mechanical properties of silicone used. Soft materials have been designed for obtaining the necessary stiffness gradient in the vocal fold cross section. Moreover, the action of the cricothyroid and the thyroarytenoid muscle on the vocal fold modulation has been replicated by using a linear actuator and a shape memory alloy wire, respectively. This last activity has been carried out under the supervision of Prof. Jonathan Rossiter and Dr. Andrew Conn, at the Soft Robotics Lab, in Bristol.<br>(ii) The development of a soft manipulator as personal care robot in the framework of the I-Support research project. Soft robotics technologies have been combined in order to provide advanced manipulation capabilities to the robot, for a safe human-robot interaction. Two technological concepts have been investigated for stiffness modulation: the first one is based on the antagonistic arrangement of active elements (cables and flexible fluidic actuators); the second one combines a cable-driven mechanism with the layer jamming semi-active technology. <br>In addition to these applications, the jamming technology has been studied and used for the development of a device able to replicate the shape of an object with high accuracy, by exploiting the transition between a compliant and a rigid state. The proof of concept has been extensively tested, providing the ground to further improvements, capitalized into a patent. <br>For each application, the suitable soft technology has been chosen and designed in order to meet the technical requirements. Prototypes have been realized spending efforts in the definition of custom and reliable manufacturing procedures (of paramount importance in new technologies). Testing has been carried out with custom-designed experimental set-ups for encompassing all the hardware components. Data analysis allowed to test adequacy and ability of the technologies of meeting the stiffness requirements of the soft-bodied system.<br>